Robust spin generation in graphene layers using interfacial spin-orbit coupling*

Generation of spin currents in graphene is fundamentally important for understanding spin related phenomena as well as for spintronic applications. Electrical spin injection, wherein a charge current is applied from a ferromagnetic electrode into graphene, is widely used method to generate spin currents in graphene. However, this method requires state of the art material growth techniques to integrate the tunnel barrier at the ferromagnet/graphene interface. As an alternative, the spin orbit coupling (SOC), in a non-magnetic heavy metal or at the interface of two different materials, can induce a spin polarization owing to spin dependent scattering of charge carriers. Here we present experiments showing large spin accumulation in graphene channels induced by SOC at the platinum/graphene interface. Clean Pt/graphene interfaces are prepared by mechanically placing graphene flakes onto Pt nanowires. We will discuss the dependence of the generated spin accumulation in graphene on charge carrier density in graphene, temperature, and magnitude of charge current in the Pt. This demonstration of large spin accumulation in graphene obtained without using a ferromagnet material represents a significant advance.